232 
nervi oculomotorius and trochlearis but also by those for the efferent 
pseudobranchial artery and the pituitary vein. In Amia the corres- 
ponding region is wholly membranous, and it is subject, in other 
fishes, to ossification in different manners; the posterior portion of 
the membrane usually ossifying as a part of the prootic bone and the 
anterior portion either as the basisphenoid leg of the alisphenoid or 
as a part of the orbitosphenoid (Anus, 1897b and 1909). 
Posterior to the low prootic ridge above described, and beginning 
directly lateral to the postclinoid wall, there is, in the lateral wall of 
the cranial cavity, a large recess in which lie the foramina for the 
nervi trigeminus, facialis and acusticus, the foramina for the trigemi- 
nus and acusticus perforating, respectively, the anterior and posterior 
walls of the recess, and the foramen for the facialis perforating the 
lateral wall about midway between the other two foramina. The 
cerebral opening of this recess is more or less completely closed, in 
different specimens, by the tough glistenmg membrane that lines the 
cranial cavity, and as this membrane undergoes chondrification to a 
different extent in almost every specimen, the size and shape of the 
cerebral opening of the recess vary greatly. In one of three specimens 
that were carefully examined in this respect, it was entirely closed, 
toward the cranial cavity, by this membrane, the membrane being 
perforated, in a horizontal line, by three foramina which transmitted, 
from before backward, the roots of the nervi trigeminus, facialis and 
acusticus, the lateralis fibers that belonged to the trigeminus and 
facialis apparently accompanying their respective roots. The recess 
was accordingly, in this specimen of Chlamydoselachus, a definite 
chamber in the lateral wall of the cranial cavity. It is the trigeminus 
fossa (Bucht) of GEGENBAUR’S descriptions of other selachians, and 
is the evident homologue of the trigemino-facialis recess of my des- 
criptions of the Mail-Cheeked fishes (Auuıs, 1909, p. 44), excepting 
in that the nervus acusticus is here related to it. It can accordingly 
here be called the acustico-trigemino-facialis recess. 
In the two other specimens that were examined, the membrane 
that formed, in the first specimen, a complete mesial wall to the 
acustico-trigemino-facialis recess was imperfectly developed in its 
middle portion, the appearance bemg much as if the membrane had 
here been pushed outward (laterally) until it reached and adhered to 
the lateral wall of the recess, thus closing the foramina trigeminum 
